Health risk assessment of particulate matter 2.5 in an academic metallurgy workshop

Abstract Exposure to indoor PM2.5 is associated with allergies, eye and skin irritation, lung cancer, and cardiopulmonary diseases. To control indoor PM2.5 and protect the health of occupants, exposure and health studies are necessary. In this study, exposure to PM2.5 released in an academic metallurgy workshop was assessed and a health risk assessment was conducted for male and female students and technicians. Polycarbonate membrane filters and an active pump operating at a flow rate of 2.5 L/min were used to collect PM2.5 from Monday to Friday for 3 months (August–October 2020) from 08:00–16:00. PM2.5 mass concentrations were obtained gravimetrically, and the Multiple‐Path Particle Dosimetry model was used to predict the deposition, retention, and clearance of PM2.5 in the respiratory tract system. The risk of developing carcinogenic and non‐carcinogenic effects among students and technicians was determined. The average PM2.5 mass concentration for August was 32.6 μg/m3 32.8 μg/m3 for September, and 32.2 μg/m3 for October. The head region accounted for the highest deposition fraction (49.02%), followed by the pulmonary (35.75%) and tracheobronchial regions (15.26%). Approximately 0.55 mg of PM2.5 was still retained in the alveolar region 7 days after exposure. The HQ for male and female students was <1 while that of male and female technicians was >1, suggesting that technicians are at risk of developing non‐carcinogenic health effects compared with students. The results showed a risk of developing carcinogenic health effects among male and female technicians (>1 × 10−5); however, there was no excess cancer risk for students (<1 × 10−6). This study highlights the importance of exposure and health studies in academic micro‐environments such as metallurgy workshops which are often less researched, and exposure is underestimated. The results also indicated the need to implement control measures to protect the health of the occupants and ensure that the workshop rules are adhered to.


| INTRODUC TI ON
Air pollution is a global environmental and public health concern, and particulate matter (PM 2.5 ) has been identified as a leading contributor to poor outdoor and indoor air quality and a significant cause of cardiopulmonary disorders, lung cancer, hospitalization, and premature death. 2,3 According to the World Health Organization, air pollution is responsible for 7.3 million premature deaths and 4.3 million of these are attributed to poor indoor air quality. 2 Exposure to PM 2.5 in indoor micro-environments is suggested to be more harmful relative to outdoor environments. 4,5 This is attributable to the confined nature of indoor environments that allows the accumulation, less dilution, transformation, and dispersion of PM 2.5.
6-8 Furthermore, exposure per unit mass of PM 2.5 released from indoor sources is between two to three orders of magnitude larger than in outdoor environments. 9,10 Studies 11, 12 have found that the concentration of indoor PM 2.5 tends to be higher than the outdoor in many cases.
This is concerning given that in modern society people spend 90% of their time in confined indoor environments such as offices, classrooms, homes, and laboratories. 13,14 Buildings with natural ventilation mechanisms tend to have higher PM concentrations relative to mechanically ventilated buildings. 15 This is because the mechanical ventilation system prevents the penetration of outdoor PM into indoor micro-environments and also filters the indoor concentration. 16 In the absence of significant sources, indoor PM 2.5 concentration can be affected by PM penetrating from the outside. 17 The penetration efficiency of PM 2.5 into indoor micro-environments depends on the structure of the building, infiltration rate and ventilation mechanisms. 18 Room occupancy and movement also contribute significantly to the concentration of PM 2.5 in micro-environments. 19 Chen et al. 12 found that the concentration of PM 2.5 in four laboratories at the National Pingtung University of Science and Technology increased by 4.9-fold during classes and decreased significantly during recess. This also indicates that academic micro-environments such as workshops are significant sources of PM 2.5 and exposure is likely to occur.
Exposure to indoor PM 2.5 is linked with allergies, 20 eye, nose, throat, and skin irritation, 21 coughing, sneezing, 22 lung cancer, 23 cardiovascular disorders, and respiratory diseases, 13,24 particularly among susceptible groups such as children, the elderly, and comorbid individuals. 13,25 Even at lower concentrations, exposure to PM 2.5 in indoor micro-environments can have adverse health effects among susceptible groups. 17 Kim and Kang 26 found that the deposition of PM is higher in individuals with comorbidities such as asthma and chronic obstructive pulmonary diseases (COPD). This is because asthma and COPD cause inflammation and narrowing of the airways. 27 On the contrary, there is a linear relationship between the obstruction of airways and the deposition of PM, which leads to significant doses. 27 Exposure can occur through dermal, ingestion, and inhalation route, however, the inhalation route has been specified as the most common and harmful route of entry. 28,29 This is because the olfactory nerves that bypass the blood-brain barrier are considered the shortest and direct pathway to the brain; therefore, particles can translocate directly into the brain. 27 The toxicity of PM 2.5 depends on the elemental composition, number concentration, particle shape and size, 27,30 whereas the severity of the health outcomes depends on the frequency and duration of exposure, concentration, individual characteristics, and route of entry. [31][32][33] Exposure to PM 2.5 can cause lung cancer irrespective of its • This is the first exposure and health study on PM 2.5 conducted in an academic metallurgy workshop in RSA.
• Using a method that considers the deposition fraction of PM 2.5 in the human respiratory tract to conduct a health risk assessment is conservative and yields lower values compared with the conventional USEPA method.
• According to the health risk analysis, workshop technicians, particularly males are at a higher risk of developing carcinogenic health effects relative to students.

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MBAZIMA much of their time there and exposure rarely produces identifiable health outcomes until in the later stages of life. 54 Moreover, poor indoor air quality is linked with discomfort, sick building syndrome, reduced memory, productivity, and performance among occupants. 55,56 To determine the degree of health risks associated with exposure to PM 2.5 in indoor micro-environments and possible mitiga-

| Site description
The study was conducted in an academic metallurgy workshop used by students registered for the metallurgy and chemical engineering technology undergraduate degree, which is a 4-year program.
Activities in the workshop are facilitated by 3 technicians. A jaw crusher, roll crusher, and cone crusher are used to crush and reduce the size of specimens such as mineral-enriched rocks or coal to smaller sizes. Minerals such as gold, platinum, chromite, copper, and silver are deemed valuable and therefore extracted. Silica is the least valuable mineral released during the process; hence, it is not extracted. Cement is also used in the process to add strength to the specimens under investigation. The processes release PM that is suspended in the air and settles over time. The settled PM is then re-suspended by air movement and the movement of students while walking inside the workshop. The workshop is 7 × 5 m with 4 windows (Figure 1), however, the windows are never opened.
Furthermore, the workshop does not have a mechanical ventilation system. As part of entering the workshop, personal protective clothing consisting of a laboratory coat, safety shoes, mask, and goggles are mandatory. However, during a walkthrough survey, it was noticed that students and technicians were not adhering to the rules of the workshop. Few students only wore laboratory coats as part of personal protective clothing.

| Deposition
Multiple-Path Particle Dosimetry (MPPD) is a mechanistic model that can be used to predict the deposition and clearance of monodisperse and polydisperse aerosols between 1 nm and 100 μm. 57 The MPPD model was developed by the Hamner Institute for Health Sciences and the Dutch National Institute for Public Health and the Environment and is freely available from https://www.ara.

| Health risk assessment
A HRA is a tool that uses procedures and systematic approaches to assess the nature, severity, and probability of developing negative health effects due to exposure to chemical or biological stressors in the environment and manage the potential health threats. 60,61 The HRA framework has four steps, (i) hazard identification, (ii) dose-response assessment (toxicity), (iii) exposure assessment, and (iv) risk assessment. 62  The average daily dose through the inhalation route was calculated using two methods, in the first method, the ADD was calculated using Equation (2) adapted from the USEPA, 63 and the second method used Equation (3) adapted from Lyu et al. 72 and Chalvatzaki et al. 73 The difference is that Equation (3) considers the PM 2.5 deposition fraction obtained using the MPPD model while Equation (2) does not.
Where C is the PM 2.5 mass concentration (μg/m 3 ), CF is the conversion factor, IR is the inhalation rate (m 3 /h), ET is the exposure duration, EF is the exposure frequency, ED is the exposure duration, BW is the body weight (Kg), AT is the average exposure (days/years), and DF is the deposition fraction obtained using  69 The ADD for 3 and 25 years was calculated using where ADD is the average daily dose (mg/kg) calculated using Equations (2) and (3), 365 is the number of days in a year, ED is the exposure duration, and LE is the life expectancy in years. The adjusted average daily dose, which is 3 years for students and 25 years for technicians was calculated using Equation (5).
where ADD cumulative is the average daily for the specific number of years for students and technicians obtained using Equation (4) and LE is the life expectancy in days. where 5 is the RFC for diesel particulates, IR is the inhalation rate, and BW is the body. The hazard quotient (HQ) was then calculated using Equation (7) to determine the risk of developing non-carcinogenic health effects among students and technicians at the metallurgy workshop.
where ADD adjusted is the adjusted average daily dose calculated using Equation (5) and RfD is the reference dose for diesel particulates calculated using Equation (6). A HQ greater than one indicated that students and technicians are at risk of developing adverse health effects while a risk quotient less than one indicates less risk. The risk of developing carcinogenic health effects due to exposure to PM 2.5 through the inhalation route was also calculated. However, to calculate the cancer risk, the slope factor is needed, therefore, the slope for PM 2.5 was calculated using Equation (8) Where IUR is the unit risk of PM 2.5 adapted from Pope III et al. 71 BW is the body weight, and IR in the inhalation rate. The risk of developing cancer (CR) among male and female students and technicians was then calculated using Equation (9).
where ADD adjusted is the adjusted average daily dose obtained using Equation (5) and SF is the slope factor calculated using Equation (8).
The cancer risk is represented by the acceptable number of cancer cases in a population and the widely used scale of risks is 1 in million (1 × 10 −6 ), 1 in one hundred thousand (1 × 10 −5 ), and 1 in ten thousand (1 × 10 −4 ). 75

| PM 2.5 mass concentration
The PM 2.5 mass concentration results for the 3 month sampling period in the academic metallurgy workshop are presented in Table 2.

| PM 2.5 deposition
The deposition, clearance, and retention of PM 2.5 into the respiratory tract of exposed students and technicians simulated using the MPPD In Figure 3D, the clearance of PM 2.5 in mg/day in the alveolar region is shown and it can be observed that the clearance occurred slowly. After 2 days of exposure, approximately 0.00032 mg was cleared in the alveolar region. From Figure 3D, it can be observed The slow clearance of particles in the alveolar region can be attributed to two natural mechanisms. The first is the absorptive mechanism whereby the PM is removed either by lymphatic transport or blood uptake, and the second is the non-absorptive mechanism in which phagocytosis and macrophages are involved. 79 These mechanisms are extremely slow; hence, the clearance can take days to months whilst other fractions of PM translocate to vital organs. 79 Furthermore, the alveolar region has a long residence time, and the alveolar sacs and alveoli are tiny, hence, only a small fraction of the particles can be exhaled. Table 3 presents the risk of developing non-carcinogenic health effects among students and technicians obtained using Equations (2) and (3). Notably, the ADD and ADD adjusted were higher for technicians than for students when using both equations. However, when using Equation (2), the ADD and ADD adjusted for both male and female students and technicians were higher than when using Equation (3) that accounted for the deposition of PM 2.5 particles into the respiratory tract. When using Equation (2), the ADD for male and female students and technicians was 3.6-fold greater than when using

| Health risk analysis
Equation (3). The ADD adjusted for male and female students was 3.6fold greater when using Equation (2)  Similarly, the HQ for male and female students and technicians was higher when using Equation (2) than Equation (3) as shown in Table 3. However, the HQ for male students was 1.39-fold greater than that of female students when using both Equations. When using Equation (2), the HQ of male and female students was 11.3fold greater than Equation (3); nonetheless, the HQ was less than one when using both equations, implying that the students were not at risk of developing non-carcinogenic health outcomes. The HQ for male and female technicians was 2.4-fold greater when using Equation (2) compared with Equation (3). The HQ of male and female technicians was higher than one when using Equation (2)  Therefore, it is not surprising that in this study, Equation (3) which accounted for particle deposition yielded lower estimates relative to Equation (2). The results of this study are consistent with Chalvatzaki et al. 73 who also found lower estimates when using Equation (3) and concluded that the equation preserves values lower than one when calculating the ADD. Table 4 shows the risk of developing carcinogenic health outcomes because of exposure to PM 2.5 calculated using Equations (2) and (3). The cancer risk of male and female students was acceptable and insignificant (<1 × 10 −6 ) when using Equation (2)

| Strengths and limitations
This is the first exposure and health study conducted during experimental activities in an academic metallurgy workshop in RSA. For improvement, future studies must consider taking personal measurements and air exchange rates and measuring for longer periods to get a better representation. 96 Future studies should also obtain a measurement from the breathing zone and consider using questionnaires to document health effects among occupants and conduct spirometry tests, particularly on workshop technicians.
Task-based sampling must be conducted to check which equipment or processes emit significant concentrations of PM 2.5 so that they can be prioritized when implementing control measures. The elemental composition and morphology of the particles in academic metallurgy workshops must be investigated since the health effects of exposure to PM depend on the size and chemical composition of the particles.

| CON CLUS ION
Exposure to indoor PM 2.5 is a global public health concern because of the associated adverse health effects. This study assessed exposure to indoor PM 2.5 for 3 months in an academic metallurgy workshop and conducted a HRA using two equations. The head region accounted for most of the deposited PM 2.5 and particles deposited in the alveolar region were still retained 7 days after exposure.
Equation (3), which accounted for the deposition fraction of PM 2.5 into the human respiratory tract, yielded lower results relative to the USEPA equation that did not account for the deposition rate.
Compared with students, technicians were at a higher risk of developing non-carcinogenic health effects. However, male technicians were at a higher risk relative to females. Male and female technicians were also at risk of developing carcinogenic health effects however, there was no risk of developing carcinogenic health effects in students. Control measures must be implemented, and workshop rules must be followed to protect the health of occupants. Despite the limitations, this is the first study to provide insight into exposure to indoor PM 2.5 in an academic metallurgy workshop in RSA and gives direction for future research in academic metallurgy workshops.

AUTH O R CO NTR I B UTI O N S
The author was solely responsible for the conceptualization, methodology, data collection, data curation, data analysis, software, visualization, and writing, reviewing and editing the first and final draft of the manuscript.

ACK N OWLED G M ENTS
Many thanks to the occupational hygiene section at the National Institute for Occupational Health for their support with sampling equipment. The author is thankful to the workshop technicians for granting permission and providing the required information.
Appreciation to China Seremi Mooa for assisting with the data analysis and Yonda "YoYo" Nokhwethu for proofreading the manuscript. The author is grateful to Thokozani Patrick Mbonane for lending a laptop to complete this manuscript. The author is also thankful to the anonymous reviewers for their polite comments and constructive criticism of the earlier versions of the manuscript.

CO N FLI C T O F I NTE R E S T
The author has no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.